A large, rapidly moving mass that strikes the Earth would be certainly capable of causing a mass extinction event. However, such a theory would require strong evidence of periodic impacts, which Earth doesn’t seem to have. Image credit: Don Davis / NASA.

Are Mass Extinctions Periodic? And Are We Due For One?

65 million years, an impact wiped out 30% of all life on Earth. Could another one be imminent?

“That which can be asserted without evidence, can be dismissed without evidence.” -Christopher Hitchens

65 million years ago, a massive asteroid, perhaps five to ten kilometers across, struck the Earth at speeds in excess of 20,000 miles per hour. In the aftermath of this catastrophic collision, the giant behemoths known as the dinosaurs, which had dominated the Earth’s surface for over 100 million years, were exterminated. In fact, around 30% of all species currently existing on Earth at the time were wiped out. This wasn’t the first time Earth had been struck by such a catastrophic object, and given what’s out there, it likely won’t be the last. An idea that’s been considered for some time is that these events are actually periodic, caused by the Sun’s motion through the galaxy. If that’s the case, we should be able to predict when the next one is coming, and whether we’re living in a time of severely increased risk.

Getting hit by a giant piece of fast-moving space debris is always a danger, but the danger was greatest in the early days of the Solar System. Image credit: NASA / GSFC, BENNU’S JOURNEY — Heavy Bombardment.